1. Field of the Invention
The present invention relates to systems and methods for reducing fuel vapor produced by stored fuel.
2. Background Art
Evaporation of fuel in a fuel tank produces fuel vapor that must be managed to reduce or eliminate releasing of the vapor to the atmosphere. Modern automotive fuel systems have a complex system that typically includes a vapor recovery canister to capture and subsequently purge fuel vapors. While this technology has evolved to an efficient and effective system for managing fuel vapor in vehicles powered by a conventional internal combustion (IC) engine, it is not readily amenable for use in hybrid electric vehicles that utilize an IC engine and an electric motor, particularly during periods when the vehicle is operating with the IC engine off. The IC engine in a hybrid electric vehicle may run only 50% or less of a typical driving cycle yet the amount of fuel vapor that needs to be managed is similar to a conventional IC engine vehicle.
A number of solutions have been proposed to reduce fuel vapor generation that include a bladder or other flexible barrier to separate the liquid fuel from the surrounding fuel vapor in the fuel storage tank, such as disclosed in U.S. Pat. Nos. 5,056,493; 5,596,971; 5,722,374; and 6,260,544, for example. While suitable for many applications, these solutions typically require more sophisticated control and increased complexity with an associated increased cost while reducing the available volume for fuel. In addition, these solutions must be integrated into the vehicle fuel control system and are not amenable to use in existing fuel systems.